Isochrone based on a route line?

Hi guys, i was wondering if its possible to calculate an isochrone area based on a route line? i like to calculate the time u spend on retouring from a route to get to a specific place. i couldnt get it working so now i solved it with blocksystem, i found on an old goolge lib. but i think isochrone can do a much more detailed job.

any idea how to do this?

thanks